Whistleblower.org defines a whistleblower as: "An employee who discloses information that s/he reasonably believes is evidence of illegality, gross waste or fraud, mismanagement, abuse of power, general wrongdoing, or a substantial and specific danger to public health and safety. Typically, whistleblowers speak out to parties that can influence and rectify the situation. These parties include the media, organizational managers, hotlines, or Congressional members/staff, to name a few."
In the context of exopolitics whistleblowers are considered a primary source of information about covert projects allegedly involving extraterrestrials or their technology, and/or individuals claiming to have experienced extraterrestrial contact.
The Exopolitics Institute, the Disclosure Project, and Project Camelot all gather information provided by whistleblowers.